1. Field of Invention
The present invention relates to a ball bearing assembly, particularly to an antifriction linear ball bearing assembly for longitudinally moving a shaft without friction within an outer sleeve.
2. Description of Prior Art
A great Variety of devices exist for enabling a shaft to move longitudinally within a sleeve. These devices generally comprise linear ball bearing assemblies. One such assembly, which is described in U.S. Pat. No. 3,884,537 to McClosky, 1975, is adopted for mounting on a circular shaft and comprises an outer sleeve and a concentric inner sleeve. The inner sleeve has a number of tracks that define paths for the circulation of balls between the sleeve and the shaft during movement of the sleeve along the shaft. The shaft has a plurality of longitudinally extending shallow raceways which form bearing surfaces for the balls as they encounter the shaft and the raceways. The vertical depth of the raceway is only a fraction of the diameter of the balls. However, this bearing assembly is designed to ride on the shaft and is not suitable for moving a shaft together with its bearing support longitudinally within a stationary outer sleeve. Moreover, the assembly is expensive to manufacture since all of its parts require intricate machining.
Another linear ball bearing assembly, described in U.S. Pat. No. 2,559,292 to Ferger, 1945, consists of a shaft and an outer sleeve. Separate continuous grooves with two straight and two curved portions are machined in the periphery of the shaft, forming four raceway circuits substantially filled with bearing balls. One straight portion of each groove is shallower than the remaining portion of the groove. In another embodiment Ferger shows an assembly where the interior face of the sleeve, rather than the periphery of the shaft, contains the raceway circuits. The curved end portions of the grooves are cut, molded, or cast in separate pieces, which are then press-fitted into the ends of the sleeve. One drawback of the aforementioned bearing assembly is high manufacturing cost, since curved passages and passages with uneven depths have to be machined.